Automatically variable speed scavenge pump drive



Nov. 8, 949 J. s. HAsBRoucK 29487439 AUTOMATICALLY VARIABLE SPEED SCAVENGE PUMP DRIVE Filed Feb. 4, 1947 VAR/HEL E Spf-f@ 0 w .e av 6 7, m 0 a f. a w P 4 h 06M, Am .4 am 7 ,wa m m m in y@ f s N la Patented Nov. 8, 1949 AUTOMATICALLY VARIABLE SPEED SCAVENGE PUMP DRIVE John S. Hasbrouck, Glastonbury, Conn., assignor to United Aircraft Corporation, East Hartford, Conn., a corporation of Delaware Application February 4, 1947, Serial No. 726,427

6 Claims. (Cl. 103-11) This invention relates to a pumping apparatus which is particularly adapted for scavenging oil in aircraft engines.

An object of this invention is to provide improvements ina scavenge oil pumping apparatus of the type disclosed in the application of Albert M. Rockwell, Serial No..726,314, filed February 4, 1947.

Another object is to provide improved means for'preventing aeration of the oil in an engine lubricating system.

Another object is to provide an improved apparatus for pumping liquid from a sump in which the capacity of the pumping apparatus is automatically varied in accordance with changes in the level of the liquid in the sump.

Another object is to provide improved means for controlling the speed ratio of a variable speed pump drive.

A further object is to provide an improved control device for automatically increasing or decreasing the capacity of a pump in accordance with variations in pumping requirements.

Other objects and advantages will be apparent from the specification and claims and from the accompanying drawing which illustrates what is now considered to be the preferred embodiment of the invention.

In the drawings, Fig. 1 is a longitudinal crosssectional View of an aircraft engine scavenge oil pumping apparatus 'constructed according to the teaching of the present invention.

Fig. 2 is a transverse cross-sectional view on a reduced scale along the line 2-2 in Fig. 1.

Fig. 3 is a view like Fig. 2 but taken along the line 3-3 in Fig. 1.

Fig. 4 is a view like Fig. 2 but taken along the line 4-4 in Fig. 1.

In aircraft engine lubricating systems drain oil usually ows by gravity to a sump and from there it is returned by a scavenge oil pump to the oil tank. Such pumps are made of excessively large capacity, in order to make sure that the drain oil does not exceed a safe level in the sump even under the most adverse operating conditions. Consequently, under most operating conditions, the sumps are kept practically dry and much air is pumped along with the drain oil and becomes mixed therewith. The resulting aeration of the oil is particularly disadvantageous in aircraft engine lubricating systems, and at high altitudes.

According to the present invention a pumping apparatus is provided which may be made large enough in capacity to prevent the liquid in a t reservoir, such as an engine drain oil sump, from exceeding a safe level under any operating conditions and which can be automatically adjusted to a lower capacity before the liquid level in the reservoir is reduced to a point Where an appreciable amount of air is pumped or mixed with the oil.

In the embodiment of the invention illustrated in the drawing a scavenge pump is driven at a Variable speed which is automatically regulated in accordance with changes in the level of the oil in the sump. The main pump is of the gear type; its speed is controlled by a reaction device in the form of Ian auxiliary gear type pump.

Referring to the drawing, a variable speed drive I0, an auxiliary or control pump I2 and a main gear type pump I4 are all housed in a casing I6 comprising a body I8 and a cap 2D. The body and cap are fastened together by bolts 22, which also lretain the casing in fluid tight engagement with the Walls (partially shown at 24) of an engine oil sump. The upper portion of casing I6 projects into the sump through a circular opening 26 in the bottom wall 24.

Drain oil from the engine (not shown) collects in the lsump chamber C on the upper side of wall 24 at a rate which varies with changes in engine operating conditions, such as engine speed, altitude, etc. This drain oil flows by gravity into the casing I6 through an entrance opening 28 and then through an opening 20| to the lower pump chamber 200 and through strainer 262 to pump inlet 44 from whence it is pumped by the main gear pump I4 to a conduit 30 (Fig. 3) leading t0 the engine oil tank. The oil tank and other parts of the engine oil circulating system, such as the pressure pump and pressure oil distributing passages, have not been shown because they are of conventional design.

'Main scavenge pump I 4 comprises two gears 34. 36 fixed respectively to parallel shafts 38, 40 rotatably mounted at their lower ends in bearings in the cap 2U and at their upper ends in bearings in a housing or pump case 4I. This housing is fastened to cap 2D by bolts 43 (Fig. 3). Rotation of shaft 40 causes both of the gears 34, 36 to rotate and to pump oil from chamber 2B@ through the main pump inlet 44 to the outlet conduit 30, at a now rate dependent upon the speed of rotation of pump gears 34, 3S.

The main pump is driven through a variable speed drive I0 by a pump drive shaft 46 which is connected to the engine crankshaft by a, gear train, not shown, so that it rotates in bearing 48 at a fixed speed relative to engine speed. A bevel 3 gear 50 xed to shaft 46 meshes with a bevel pinion 52 splinedat 54 to a stub shaft 56. The stub shaft extends through the top of casing I8 and is supported by a ball bearing 58 in an opening n the top of the casing. It is integral with a cup or hub member 59, located within the top portion of the casing. A bevel driving gear 64 is pinned at 65 to hub 56. An annular one piece cage 63 carries a plurality of shafts 6l which support v bushings 51 on which planet pinions 62 are rotatably mounted. These planet pinions mesh on their upper sides with the bevel ring drive gear 64, and on their lower sides with a bevel ring reaction gear 66 which is pinned at 61 to a collar 55 which in turn is pinned at 53 to drive shaft 68 of the control pump I2. Shafts 56, and 68 are coaxial, with the upper end of the main pump drive shaft 46 journaled at 45 within the lower end of the stub shaft 56 and with the control pump drive shaft 68 rotatably mounted at 12, 14 on the shaft 46. The cage 63 is keyed at 5I to the main pump shaft 48 and the planet pinion shafts 6I are mounted in radial openings in the cage on axes normal to the axis of shaft 48. The pinion shafts are pinned to the cage at 68. The variable speed drive lil thus constitutes a planetary or differential gear having a cage 65 for driving the main pump i4 and a reaction gear 66 for driving the control pump I2. The cage and reaction gears are both driven through the bevel ring drive gear 64 and engine driven shaft 46.

The control pump is preferably of the gear type, comprising a pair of intermeshing gears 1 I, 13 respectively mounted on the shaft 58 and a shaft 68. journaled in a partition 1li extending across the casing I8 just below the bottom wall of the sump. Their upper ends are journaled in a cap piece 16 which is fastened to the partition. The partition and cap cooperate to form a housing or pump .L

case for the gears 1 I, 13'of the control pump, the gears being located in a recess in the partition underneath the cap. As shown in Figs. 4 and 2, the cap 16 is provided with an inlet passage 18 and an outlet passage 82 for the control pump I2. The inlet openings 18, 52 for these passages both lie in a horizontal plane indicated by the broken line 18. The inlet passage 18 may have a screen or filter 11 therein and the outlet passage 82 has inserted therein a ow restriction or orifice 84 of predetermined size and flow capacity.

With this arrangement, oil flows by gravity into the inlet 18 of the control pump whenever the oil in the sump is above the level indicated at 19. But when the oil in sump chamber C is lowered (by pump I4) so that it is near or below the level of line 18 then a mixture of oil and air, or air alone, is admitted through the inlet 18 to the pump l2. The load, or discharge pressure, on the control pump is determined by the flow characteristics of restriction 84 and the nature or condition of the fluid admitted to the pump through inlet 18. Thus, when the oil level in the sump is high and oil only is admitted to the control pump the load thereon is much greater than when the oil level in the sump is so low that air only, or mixtures or slugs of air and oil, flow through the pump inlet 18.

The reaction created by the control pump I2 (or the torque required to drive it) is transmitted between the pump and the reaction gear 66 through shaft 68 and collar 55. Consequently the reaction or braking effect of the gear 66 is a function of the load on pump I2, which in turn is determined by the level of the oil in the sump and The lower ends of these two shafts are the characteristics of the flow restriction 82. A change in oil level which alters the load on the control pump will, therefore, vary the speed of rotation of the reaction gear 66 and thereby alter the speed ratio of the planetary drive so as to change the speed of the main scavenge pump I4. The arrangement is such that when the oil is below the predetermined level 16 the main pump I4 is decreased in speed, and therefore in capacity. When the oil is above this predetermined level the main pumpk is increased in speed and capacity. Under any conditions, oil only is admitted to the main pump as long as any oil is present in the sump because the entrance opening 28 extends to the bottom wall of the sump and the chamber 206 is located below this bottom wall.

Operation When the engine is started, the driving shaft 46 begins to rotate at a predetermined speed relative to engine speed. Assuming the sump C is dry, there will be little or no load on the control pump l2 and consequently shaft 68 and reaction gear 66 will rotate relatively freely and rapidly, thereby reducing the speed of the main gear pump i4 to either zero or a relatively low value.

As the sump begins to lill, oil flows through the openings 28 and 28| and lls the lower pump casing chambers 266. If the sump continues to ll, the oil reaches or exceeds the level 19 and flows into the pump I2 through the inlet opening 18. The resultant increase in discharge pressure (created by oil flow through orifice 84) considerably increases the torque required to drive the control pump and thereby reduces the speed of the reaction gear 66 and increases the speed of cage 63 and the main pump i4. Thus, when the fluid flowing through the control pump inlet 16 is all air the control pump rotates relatively fast and the main pump rotates relatively slow, or is stationary. When the fluid flow through the inlet 18 is all oil then the control pump rotates relatively slow and the main pump relatively fast. Under other conditions, for instance when the oil is at or very near the level 19 or when the inlet uid is mixed liquidand gas or rapidly alternating liquid and gas, then the control pump and main pump will both be rotated at some intermediate speed, dependent on the relative amounts of liquid and gas flowing through the control pump inlet.

The planetary drive I8, control pump I2 and main pump I4 are preferably so designed that when the oil level in sump C is high (considerably above the level 19 of inlet opening 18) the main pump, which will then be operated at maximum speed, will have suflicient capacity to lower the level of the oil in the sump for any engine operating condition. In other words, the capacity of the pumping apparatus at maximum speed of pump i4 is greater than the maximum inflov'y of drain oil to sump C. Thus the quantity of oil in the sump can never exceed a predetermined safe limit. But when the quantity of oil in the sump decreases to a level near or below the plane of line 19 then a material quantity of air is admitted through inlet 13 along with the oil and the load on the control pump I2 is relieved, enabling reaction gear 66 to rotate more rapidly and causing the cage 63 and the main pump I4 to be driven more slowly, thereby decreasing the speed and capacity of pump I4 and reducing the rate of oil fiow through the pumping apparatus to a value commensurate with pumping requirements.

The automatic variation of pumping capacity with pumping requirements according to the present invention not only tends to eliminate aeration of the lubricating oil but also improves pump stability and efficiency, saves power and provides other advantages 0f particular importance in aircraft engine lubricating systems.

It is to be understood that the invention is not limited to the specific embodiment herein illustrated and described, but may be used in other ways without departure from its spirit as defined by the following claims.

I claim:

1. In an oil scavenging apparatus for aircraft engines, a scavenge pump, and means including a gear type control pump for regulating the capacity of said scavenge pump, said gear type control pump being arranged to use only a portion of the fluid that flows into said scavenge pump.

2. Means for preventing aeration of the liquid in a liquid circulating system comprising, a liquid container, a pump having an inlet passage communicating with said container for evacuating liquid from said container, means for controlling the rate at which liquid is evacuated from said container by said pump, and means for maintaining a continuous supply of liquid at the point where said scavenge pump inlet passage communicates with said container comprising level detecting means for actuating said controlling means to reduce said rate of evacuation when the quantity of liquid in said container falls below a predetermined amount.

3. In an automatically variable speed pump drive, a planetary transmission having a main pump drive gear and a reaction gear, and means comprising a control pump and a 110W restriction connected in series for controlling the speed of the main pump drive gear by varying the braking effect of the reaction gear.

4. In combination, a pair of pumps having inlet passages" for respectively receiving fluid from a containerat different predetermined levels therein, and a transmission for driving one of said pumps at a speed dependent on the amount of entrained air in the uid admitted through one of said inlet passages to the other of said pumps.

5. An oil scavenging apparatus for an aircraft engine having a crankshaft comprising, an oil sump, a scavenge pump for withdrawing oil from said sump, a transmission for driving said scavenge pump by said crankshaft, and means including a control pump having inlet and outlet passages communicating with said sump for regulating the speed of said scavenge pump relative t0 said crankshaft.

6. Appratusaccording to claim 5, including a restricted orifice in said control pump outlet passage.

JOHN S. HASBROUCK.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS 

